To evaluate the differences between treatment groups in: The change of mean trough sitting diastolic blood pressure (SDBP) after 8 weeks of active treatment. The change of mean trough sitting systolic blood pressure (SSBP) after 8 weeks of active treatment. The change of mean trough sitting diastolic blood pressure (SDBP) after 4 weeks of active treatment. The change of mean trough sitting systolic blood pressure (SSBP) after 4 weeks of active treatment. To describe the mormalization rate and the response rate for each treatment group. To describe safety of mibefredil with that of verapamil SR through monitoring of adverse events and heart rate.